This invention relates generally to meteorological instruments, and more particularly to a rainfall rate gauge or meter capable of measuring very light to very heavy rainfalls.
Meteorologists, forest rangers and others require accurate rainfall meters, which will work unattended, for the most part, and will store information about rainfall history. A number of devices suitable for this purpose are well known. One type of rainfall gauge has one or more buckets which fill with water as rain falls on a collection funnel above the bucket. See U.S. Pat. No. 4,644,786, for example. When the bucket has filled to a certain point, it becomes unstable and tips sideways, discharging the contents. A mechanical or electrical device may note this event in a recorder of some sort.
Conventional pivoting bucket-type rain gauges are not well suited for measuring very low rainfall rates. Once the time required to fill the bucket exceeds the sampling interval, the measurement loses some of its meaning.
In arid areas, even slight rain may strongly influence the environment. The combustibility of ground materials, for example, can be greatly affected by light rain. We thus consider it important to improve on the accuracy and sensitivity of bucket-type rainfall meters.
Some prior inventors have proposed replacing the pivoting rain buckets with a turbine wheel, so that the weight of the water in the recesses on one side of the turbine causes the wheel to rotate. See U.S. Pat. Nos. 3,127,769 and 3,978,723 for examples. Friction is a critical variable for such devices, since they are not positively displaced. A lower friction turbine turns more rapidly than does one with higher friction, all other factors being equal, since the turbine buckets need not be filled any particular amount in order to rotate the turbine. For very small gauges, surface tension effects can also provide substantial uncertainty.